Melt the butter in a large (8-10 Quart) kettle over medium heat. Add the onion, leeks, carrot and celery. Cook, stirring often, until the onions are soft but not browned. Add the chicken pieces, parsley, thyme, peppercorns, bay leaf, marjoram and water. Slowly bring to a boil. Reduce heat. Cover. Simmer until the broth develops a rich flavor (3 1/2-4 hours). Strain. Discard the solids. Return to the kettle. Boil gently, uncovered, until reduced to the final quantity (30-60 minutes). Taste. Season with salt to taste. Refrigerate overnight. Skim off and discard fat. Use within 3 days.